Conventionally, a position specifying apparatus that specifies a position of an image probe on the basis of a two-dimensional code and a quasi-random pattern drawn on a two-dimensional scale is known. For example, Japanese Patent No. 4463612 discloses a position specifying apparatus that i) specifies a position of an image probe by detecting a two-dimensional code and a quasi-random pattern drawn on a two-dimensional scale using an image probe and by specifying position information on the two-dimensional scale included in the two-dimensional code, and that ii) specifies a position of the image probe on the two-dimensional scale by calculating a relative position of the quasi-random pattern from a center of a field of view corresponding to the image probe on the basis of an image correlation between the quasi-random pattern and a template image.
Because the conventional position specifying apparatus reads the two-dimensional image arranged in a lattice pattern on the two-dimensional scale using the image probe, the time required for specifying the position on the two-dimensional scale was determined by the reading speed of the image probe. Further, when the amount of data for specifying the position is large, the area of the pattern image included in the two-dimensional code becomes large, and so the reading time of the image probe in the conventional position specifying apparatus becomes long. As a result, it took a long time to specify the position. Therefore, there is a demand to shorten the reading time of the two-dimensional code on the two-dimensional scale.